A ferromagnetic thin film of Fe, FeCo, or the like is often used as an electrode material of a tunnel magnetoresistive (TMR) element or a current perpendicular to plane-giant magnetoresistance element. Many of these ferromagnetic materials have body-centered cubic lattice (bcc) structures. These magnetoresistance elements are used for a reproduction head of a hard disc drive (HDD) or a recording element of a magnetoresistance random access memory (MRAM). In addition, a current perpendicular to plane-giant magnetoresistance (CPP-GMR) element having a Co-based Heusler alloy having a high spin polarizability as a ferromagnetic layer has a lower element resistance than a tunnel magnetoresistance element, and therefore application thereof as a magnetic head for a next-generation high density HDD is expected strongly (refer to Patent Literatures 1 and 2).
However, all of these magnetoresistance elements in practical use have polycrystalline structures. For example, a tunnel magnetoresistance element in which magnesium oxide (MgO) is a tunnel barrier using a CoFeB ferromagnetic material as an electrode is formed by the following manufacturing process.
(i) Amorphous CoFeB is formed on amorphous Ta formed on a Cu electrode.
(ii) A MgO tunnel barrier growing in a strong (001) orientation is formed on the amorphous CoFeB in (i).
(iii) Amorphous CoFeB is further formed on the MgO tunnel barrier in (ii).
(iv) The above formed multilayer film is subjected to a heat treatment, and the amorphous CoFeB is crystallized into CoFe having a body-centered cubic lattice structure.
(v) At this time, each crystal in the polycrystal has a consistency relation of (001)[001]CoFe//(001)[011]MgO using a Miller index, and therefore a tunnel electron is spin-polarized highly.
A high tunnel magnetoresistance is exhibited by (i) to (v).
Each crystal in a polycrystal crystallized from amorphous FeCoB is required to have a consistency relation of (001)[001]CoFe//(001)[011]MgO with an oxide barrier such as MgO or MgAlO in order to obtain a high tunnel magnetoresistance. Recently, a tunnel barrier of MgAl2O4, non-stoichiometric MgAlO, or the like is used in addition to MgO. In any case, in order to exhibit a high tunnel magnetoresistance, a ferromagnetic body having bcc as a basic structure, such as Fe, Co, an alloy thereof, or a Co-based Heusler alloy is required to be oriented in a (001) direction of a Miller index.
Meanwhile, a current perpendicular to plane-giant magnetoresistance (CPP-GMR) element has a structure in which a laminated film of ferromagnetic layer/non-magnetic layer/ferromagnetic layer is formed into a pillar having a submicrometer-size or less. When a current flows in a pillar, an electric resistance is changed according to a relative angle of magnetization of two ferromagnetic layers, and therefore a magnetic field can be detected electrically. However, when a general ferromagnetic body such as CoFe is used, a magnetoresistance (MR) ratio is about 3% (refer to Non-patent Literature 1), and a low sensitivity as a magnetic sensor is a problem. However, recently, in an epitaxial CPP-GMR element of Heusler alloy layer/non-magnetic layer/Heusler alloy layer, obtained by growing a Co-based Heusler alloy (Co2MnSi, Co2(Fe0.4Mn0.6)Si, Co2Fe(Ga0.5Ge0.5), or the like) having a high spin polarizability on a MgO substrate as a ferromagnetic layer, a magnetoresistance ratio as large as 30 to 60% has been achieved (refer to Non-patent Literatures 2 to 4). There is no other example of such a magnetoresistance element having a low resistance and a high magnetoresistance ratio, and application thereof to various devices such as a read head for a next-generation hard disc drive (HDD), having a surface recording density of 2 Tbit/inch2 or more is expected highly.
However, an element utilizing a Heusler alloy electrode has such a serious problem that a high characteristic of a MR ratio of more than 30% can be obtained only when a (001)-oriented monocrystalline thin film manufactured on an expensive (001)-MgO substrate is subjected to a heat treatment at 500° C. or higher. It is known that when a polycrystalline element is manufactured on a generally used Si substrate with a thermal oxide film, a characteristic thereof is much poorer than that of a monocrystalline element (refer to Non-patent Literature 5). In addition, it has been reported that in a monocrystalline CPP-GMR element having a Heusler alloy as a ferromagnetic layer and having Ag as a spacer layer, a MR ratio largely depends on a crystal orientation and the highest MR output is obtained when a ferromagnetic layer is oriented in a (001) plane (refer to Non-patent Literature 6). A polycrystalline magnetoresistance element oriented in a (001) plane has been also proposed due to such a background (Patent Literature 3). It is necessary to manufacture a magnetoresistance element on a permalloy layer which has been electrodeposited as a magnetic shield for application to a currently used read head for HDD. In this case, a ferromagnetic layer is a polycrystal oriented in (011). In addition, when a heat treatment is performed at 350° C. or higher, diffusion of a permalloy layer, recrystallization, or the like occurs disadvantageously. Because of these, if a monocrystalline element having a ferromagnetic layer oriented in (001) can be grown on an inexpensive Si wafer, it is expected that a magnetoresistance element having a large MR ratio can be achieved.